The present invention relates to an apparatus for controlling an elevator that is driven by an induction motor.
FIGS. 8 and 9 show a prior-art apparatus for controlling an A.C. elevator disclosed, for example, in Japanese Utility Model Application Laid-open No. 60-12568. FIG. 8 is a circuit diagram of a block diagram of the control apparatus, and FIG. 9 is a vector diagram.
In FIGS. 8 and 9, numeral 1 designates a three-phase A.C. power source. 2 denotes A.C. reactors connected to the A.C. power source 1. Numeral 3 indicates a converter which converts an A.C. into a D.C. by a pulse width modulation. The converter 3 has transistors connected at its input side to the A.C. reactors 2 to receive input currents and diodes in parallel with the transistors. Symbols 4A to 4C depict current detectors for detecting the input currents of the converter 3. Numeral 5 designates D.C. buses connected to the output side of the converter 3, numeral 6 denotes a D.C. voltage detector for detecting a voltage between the D.C. buses 5. Numeral 7 indicates a reference voltage setter. Numeral 8 depicts a voltage control amplifier, numeral 9 designates a three-phase sinusoidal wave oscillator. Symbols 10A to 10C denote multipliers. Symbols 11A to 11C indicate current control amplifier. Numeral 12 depicts a saw-tooth wave generator. Numeral 13 designates a comparator. Numeral 14 denotes a base driving circuit for producing a signal to the buses of the transistors of the converter 3. As will be shown, the D.C. buses 5, 5 are connected to an inverter constructed in the same manner as the converter 3, and a three-phase induction motor for hoisting an elevator is connected to the output side of the inverter.
The prior-art apparatus for controlling the A.C. elevator is constructed as described above, and the operation of the apparatus will be described herebelow.
The A.C. voltage from the A.C. power source 1 is converted by the converter 3 into D.C., which is, in turn, supplied to the inverter, and the voltage between the D.C. buses 5 and 5 is detected by the D.C. voltage detector 6. The voltage control amplifier 8 compares the D.C. voltage signal 6a with the output of the reference voltage setter 7 and generates a current command signal. The output of the voltage control amplifier 8 is multiplied by the multipliers 10A to 10C by the outputs of the sinusoidal wave generator 9, and sinusoidal current command signals are generated. The sinusoidal current command signals from the multiplier 10A to 10C are, in turn, applied to the current control amplifiers 11A to 11C. On the other hand, the outputs of the current detectors 4A to 4C are also applied to the current control amplifiers 11A to 11C. Thus, the current control amplifiers 11A to 11C calculate and amplify deviations between the current command signals of the outputs of the multipliers 10A to 10C and the outputs of the current detectors 4A to 4C, respectively. The outputs of the current control amplifiers 11A to 11C are then applied to the compartor 13. On the other hand, the output of the saw-tooth wave generator 12 is also applied to the comparator 13. Thus, the comparator 13 compares the outputs of the current control amplifiers 11A to 11C with the output of the saw-tooth wave generator 12, and generates pulse-width modulation signals. These pulse-width modulation signals are amplified by the base driving circuit 14, and, in turn, applied to the bases of the transistors of the converter 3 as base signals to control the converter 3, thereby controlling to maintain the voltage of the D.C. buses 5 constant.
The current command signals applied to the bases of the transistors of the converter 3 for controlling the converter 3 in FIG. 8 are sinusoidal. Accordingly, the input currents to the converters 3 also are sinusoidal, and the following vector equation is satisified. EQU Vin=Vac+jXI (1)
wherein
Vin denotes an input voltage of the converter 3, PA1 Vac denotes a voltage of the A.C. power source 1 PA1 I denotes an input current of the converter 3, and PA1 X denotes an impedance of the AC reactor 2.
In order to improve the power factor, the input current I must be set in phase with the AC voltage Vac. At this time, as shown in FIG. 9, the A.C. voltage Vac crosses the voltage drop XI of the A.C. reactor 2. Therefore, the following equation is satisfied. ##EQU1##
Since the peak value of the input side voltage of the converter 3 cannot be raised to a value higher than the D.C. voltage Vd, it is necessary to select the D.C. voltage Vd to satisfy the following formula so as not to include harmonic components. ##EQU2##
In order to control the phase of the input current I of the converter 3 in phase with that of the power source voltage VAC so as to reduce the harmonic wave components of the input current of the converter 3 and to improve the power factor in the prior-art apparatus for controlling the A.C. elevator, it is necessary to raise the input voltage of the converter 3 to a value indicated by an input voltage Vin1, when a load current is large, and to a value indicated by an input voltage Vin2, when the power source voltage is varied to a higher value. To this end, the prior-art apparatus has such drawbacks that the voltage of the D.C. buses 5 must be raised and high dielectric strength components must be employed.